HOW TO HIDE USER NAME

hI: I just went under the FAQ to answer a question: How do I prevent my username from appearing in the online user listings? The answer given was:In your profile you will find an option Hide your online status; if you switch this on you'll only appear to board administrators or to yourself. You will be counted as a hidden user.Problem: I went under profile, and there was no option that said "hide your online status" Where can I find this? thanks